The invention relates to an electrical power supply system for an electrically powered motor vehicle, to a method for controlling such a power supply system, and to an electrically powered motor vehicle including such an electrical power supply system.
In order to approach the comfort and performance of motor vehicles having internal combustion engines, in terms of speed, acceleration, and range, it is known that electric vehicles can be equipped with batteries of the Lithium-metal-polymer type whose performance levels are considerably higher than those offered by previous-generation technologies, and in particular by the Ni—Cd batteries of “first-generation” electric vehicles.
However, acceleration and driving at high speeds cause such a battery to be discharged considerably due to the high power levels required by the motors of such electric vehicles. Such considerable discharging deteriorates batteries of the Lithium-metal-polymer type, and considerably reduces their lives.
Batteries of the Lithium-ion type are capable of delivering very high currents without any significant degradation in their performance.
However, batteries of that type have low energy per unit volume, and are more costly than batteries of the Lithium-metal-polymer type.
Therefore, in view of the constraints in terms of compactness and cost, use of them for powering the electric motor of a motor vehicle does not make it possible to obtain energy sufficient to achieve the objectives of range and of comfort.
In addition, the accessories, in particular the air-conditioning device, require a large quantity of electrical energy.
Document U.S. Pat. No. 5,796,175 discloses an electrical power supply system for an electrically powered motor vehicle, said vehicle including an electric motor, a transmission device for transmitting energy between the drive wheels and the motor, and electrical accessories, in particular an air-conditioning device, said system comprising a first rechargeable battery serving to power the electric motor and a second rechargeable battery serving to power the electrical accessories of the vehicle.
Document WO 03/023934 discloses a switch device for switching between two batteries for starting a motor vehicle. However, that document does not suggest using such a switch for traction of an electric vehicle, which, as indicated above, poses particular problems in terms of comfort and of performance, in particular because the energy necessary for the electric motor varies.